Update Wormblight to check if target is summoner of source to decide healing

Update Wormblight to check if the target is the summoner of the source to determine healing, rather than checking for the 'worm' attribute granted by the Infestation sustain. Now the talent will only heal the summoner of the worms, as you would expect from the talent description, and will continue healing even if the sustain is no longer active.

See merge request !677